Diversification and a high penetration rate of radio communication devices and an increase in content are factors increasing traffic of a wireless network. Radio communication techniques have progressed in a direction for raising a data transmission rate in order to solve the traffic problems of the wireless network.
The Long Term Evolution (LTE) system is a representative radio communication system commercialized in an attempt to raise the data transmission rate. The LTE system has developed toward improving spectral efficiency in order to increase the data transmission rate. However, there is difficulty in satisfying demands for the wireless data traffic only by improvement of the spectral efficiency.
A way to solve the problem is to use a wide frequency band. However, current radio communication systems using a frequency band of 5 GHz or lower have difficulty in securing the wide frequency band. Thus, it is necessary to secure a wideband frequency in a higher frequency band.
In general, path loss is increased with a transmission frequency raised in the radio communication systems. Distance of arrival for determining radio communication service coverage is reduced due to the increase of the path loss. Beam-forming techniques alleviate the propagation path loss to increase the distance of arrival in the radio communication systems.
Among the beam-forming techniques, a transmission beam-forming technique concentrates signals transmitted from a plurality of antennas to a specific direction. Here, each of the plurality of antennas is called an antenna element. A set of the antenna elements is called an array antenna.
The transmission beam-forming technique can increase the distance of arrival of transmitted signals. The transmission beam-forming technique may also transmit signals only in a desired direction. The transmission beam-forming technique prevents signals from being transmitted in a direction other than the desired direction. This can reduce interference in the wireless network.
A reception beam-forming technique using a reception array antenna may be applied to a reception side. The reception beam-forming technique can intensively receive a radio wave introduced from a specific direction. This can increase a receiving sensitivity. In addition, the reception beam-forming technique can regard signals introduced from a direction other than a desired direction as interference to interrupt the signals.
In general, a radio signal has a short wavelength with a raised use frequency. Accordingly, in a case of configuring antennas at a half wavelength interval, an array antenna having more antenna elements in the same area may be configured to use a high frequency.
The beam-forming technique may obtain a relatively higher antenna gain in a high frequency band as compared with a low frequency band. Accordingly, it is advantageous to apply the beam-forming technique to a radio communication system using an ultra-high frequency.
However, a new beam-forming technique is needed to obtain the high data transmission rate in the multiple antenna system, together with the application of the analog beam-forming technique for acquisition of the high antenna gain.